---
id: CVE-2026-16158
title: >-
  Impact: @fastify/reply-from versions from 8.3.1 up to but not including 12.6.4
  build the internal URL cache key by concatenating the destination and source
  path without a delimiter
summary: >-
  Impact: @fastify/reply-from versions from 8.3.1 up to but not including 12.6.4
  build the internal URL cache key by concatenating the destination and source
  path without a delimiter. Different destination and source pairs can therefore
  pr…
severity: high
cvss: 8.7
cvssVector: 'CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:N'
cwe:
  - CWE-441
published: '2026-07-18'
updated: '2026-07-18'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-16158'
references:
  - url: 'https://cna.openjsf.org/security-advisories.html'
    label: ce714d77-add3-4f53-aff5-83d477b104bb
  - url: >-
      https://github.com/fastify/fastify-reply-from/security/advisories/GHSA-v574-6498-x57v
    label: ce714d77-add3-4f53-aff5-83d477b104bb
tags:
  - nvd
ingestedAt: '2026-07-19T03:27:58.168Z'
epss: 0.00231
epssPercentile: 0.14205
---

## Overview

Impact: @fastify/reply-from versions from 8.3.1 up to but not including 12.6.4 build the internal URL cache key by concatenating the destination and source path without a delimiter. Different destination and source pairs can therefore produce the same key while resolving to different upstream URLs. When getUpstream selects an upstream from request data, a URL cached for one upstream can be reused for a request intended for another upstream, causing cross-upstream data access and modification. The default configuration is affected. Setting disableCache to true prevents the behavior. Patches: upgrade to @fastify/reply-from 12.6.4. Workarounds: pass disableCache: true when registering the plugin.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.